var age = 3;
if (age >= 18) { console.log('adult');
} else if (age >= 6) { console.log('teenager');
} else { console.log('kid'); }

var arr = ['Apple', 'Google', 'Microsoft'];
for (var i = 0; i < arr.length; i++) { console.log(arr[i]); }

var o = { name: 'Jack', age: 20, city: 'Beijing' };
for (var key in o) { console.log(key); }  // 'name', 'age', 'city'

var x = 0, n = 99;
while (n > 0) { x = x + n; n = n - 2; }
console.log(x);
